1. Field of the Invention
The invention relates to a diverter valve for a variable cycle gas turbine engine, and particularly to a valve for selectively changing the flowpath of working fluid through a tandem fan engine.
2. Description of the Related Art
The present invention is particularly concerned with variable cycle gas turbine engines of the type described in our UK Patents Nos GB 1,389,347 and GB 1,415,679. These engines have a first axial flow compressor, sometimes referred to as a front fan and a core engine incorporating a further fan type compressor, thus giving rise to the idea of tandem fans. The two compressor fan stages may be driven by separate turbines.
A tandem fan engine can be operated alternatively in series-flow or parallel-flow modes. In the first the whole of flow output of the first fan is ducted to the second compressor fan thereby effectively supercharging the core engine. In the alternative the flow output of the front fan is discharged from the communicating duct and the second fan draws air into the core engine through an auxiliary inlet. The flow from the first fan may be discharged into a by-pass duct or directed to one or more discharge nozzles, these may be fixed or vectorable.
To selectively redirect the fluid flowpath in the communicating duct between the two fan stages a diverter valve is provided, together with auxiliary inlet and outlet apertures. Examples of diverter valves are described in the above mentioned patents. The present invention is intended to provide a simpler valve design which is lighter and more efficient than these earlier proposals.